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Escherichia coli normally behaves as a commensal organism and constitutes about 0.1% of the normal flora of the human gut where its beneficial properties include synthesis of vitamin K. Some strains of Escherichia coli can cause disease and these pathogenic strains have acquired various pathogenicity determinants, most likely by horizontal gene transfer. The diseases caused by Escherichia coli fall into two types: intestinal diseases and non-intestinal diseases. The latter type includes urinary tract infections and neonatal meningitis. There are seven different types of intestinal disease caused by Escherichia coli and each type is caused by a different pathovar with unique virulence determinants. Based on genome analysis, the bacteria formerly classified as Shigella species are simply pathovars of Escherichia coli. Some Escherichia coli strains can increase their virulence by inactivating certain chromosomal genes, a process known as pathoadaptation, and this may occur by movement of insertion sequences. |
